[WIP/RFC] assert: keep "where … and …" output in verbose mode

Ref: pytest-dev#5932
Fixes: pytest-dev#5192

src/_pytest/assertion/__init__.py

@@ -110,8 +110,8 @@ def pytest_runtest_setup(item):
     comparison for the test.
     """
 
-    def callbinrepr(op, left, right):
-        # type: (str, object, object) -> Optional[str]
+    def callbinrepr(op, left, right, expl):
+        # type: (str, object, object, str) -> Optional[str]
         """Call the pytest_assertrepr_compare hook and prepare the result
 
         This uses the first result from the hook and then ensures the
@@ -127,10 +127,13 @@ def callbinrepr(op, left, right):
         pretty printing.
         """
         hook_result = item.ihook.pytest_assertrepr_compare(
-            config=item.config, op=op, left=left, right=right
+            config=item.config, op=op, left=left, right=right, expl=expl
         )
         for new_expl in hook_result:
             if new_expl:
+                if isinstance(new_expl, str):
+                    return new_expl
+
                 new_expl = truncate.truncate_if_required(new_expl, item)
                 new_expl = [line.replace("\n", "\\n") for line in new_expl]
                 res = "\n~".join(new_expl)

src/_pytest/assertion/rewrite.py

@@ -392,7 +392,7 @@ def _call_reprcompare(ops, results, expls, each_obj):
         if done:
             break
     if util._reprcompare is not None:
-        custom = util._reprcompare(ops[i], each_obj[i], each_obj[i + 1])
+        custom = util._reprcompare(ops[i], each_obj[i], each_obj[i + 1], expl)
         if custom is not None:
             return custom
     return expl

src/_pytest/assertion/util.py

@@ -14,7 +14,9 @@
 # interpretation code and assertion rewriter to detect this plugin was
 # loaded and in turn call the hooks defined here as part of the
 # DebugInterpreter.
-_reprcompare = None  # type: Optional[Callable[[str, object, object], Optional[str]]]
+_reprcompare = (
+    None
+)  # type: Optional[Callable[[str, object, object, str], Optional[str]]]
 
 # Works similarly as _reprcompare attribute. Is populated with the hook call
 # when pytest_runtest_setup is called.
@@ -121,7 +123,7 @@ def isiterable(obj):
         return False
 
 
-def assertrepr_compare(config, op, left, right):
+def assertrepr_compare(config, op, left, right, expl):
     """Return specialised explanations for some operators/operands"""
     maxsize = (80 - 15 - len(op) - 2) // 2  # 15 chars indentation, 1 space around op
     left_repr = saferepr(left, maxsize=maxsize)
@@ -146,7 +148,7 @@ def assertrepr_compare(config, op, left, right):
                     type_fn = (isdatacls, isattrs)
                     explanation = _compare_eq_cls(left, right, verbose, type_fn)
                 elif verbose > 0:
-                    explanation = _compare_eq_verbose(left, right)
+                    return expl + "\n~" + "\n~".join(_compare_eq_verbose(left, right))
                 if isiterable(left) and isiterable(right):
                     expl = _compare_eq_iterable(left, right, verbose)
                     if explanation is not None:

src/_pytest/hookspec.py

@@ -472,7 +472,7 @@ def pytest_unconfigure(config):
 # -------------------------------------------------------------------------
 
 
-def pytest_assertrepr_compare(config, op, left, right):
+def pytest_assertrepr_compare(config, op, left, right, expl):
     """return explanation for comparisons in failing assert expressions.
 
     Return None for no custom explanation, otherwise return a list